The present embodiment relates to the irradiation of marked media. It finds particular application in conjunction with an irradiation system in which ultraviolet (UV) radiation is selectively applied to an imaged region of print media to fuse, cure, or dry the image. However, it is to be appreciated that the present embodiment is also amenable to other like applications.
Printing methods, such as xerographic and ink-jet printing methods, use fusing or curing as a way to provide image permanence. Ink-jet printing methods often use a water-based marking material or ink which is applied to a substrate, such as paper. The ink remains wet until air dried or heat dried. If printed pages are stacked without sufficient drying time, ink may smear or transfer to the adjacent sheet. Drying time is therefore an obstacle to high speed printing. In applications where double-side printing is used, or where printing is performed on non-absorbent substrates, the slow dry time can be an even larger obstacle to high print speeds.
UV curable inks have been developed to address problems of drying and permanence of images in ink-jet printing systems. The inks are cured with a UV flood lamp. UV curable inks have also been developed for printing systems that jet melted ink that is solid at ambient temperatures. For these inks, UV curing hardens the ink compared to its un-irradiated state, thereby improving the prints resistance to scratching, smearing, and transferring. This is particularly important for prints that may be exposed to higher pressures and/or temperatures than usual. Furthermore, the chemical crosslinking that can be achieved by UV curing can create desirable material properties for the printed ink that are not achieved with ordinary heat based curing approaches.
In typical xerographic marking devices, a dry marking material, such as toner particles adhering triboelectrically to carrier granules, is used to create an image on a photoconductive surface which is then transferred to a substrate. The toner image is generally fused to the substrate by applying heat to the toner with a heated roller and application of pressure to melt or otherwise fuse the dry marking material. The fusing process serves two functions, namely to attach the image permanently to the sheet and to achieve a desired level of gloss.
In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a corresponding color. The single color toner images are successively transferred to the copy paper to create a multi-layered toner image on the paper. The multi-layered toner image is permanently affixed to the copy paper in the fusing process.
Fusers, because of the high temperatures at which they operate and frequent heating and cooling cycles that they undergo, tend to be prone to failure or suffer reliability issues. The reliability issues are of particular concern in printing systems which employ several small marking devices. These systems enable high overall outputs to be achieved by printing portions of the same document on multiple printers in which an electronic print job may be split up for distributed higher productivity printing by different marking devices, such as separate printing of the color and monochrome pages. However, since each marking device in the printing system has its own dedicated fuser, the reliability issues are compounded.
Alternative fusers have been developed which employ light for fusing images. For example, high energy laser beams have been used to fuse toner particles.
These methods for fusing and curing images all involve exposing the entire sheet to the energy source, which is both energy consuming and generates excess energy to be dissipated by the fusing system and may also cause sheet shrinkage and or curl.